Cell Processes

Types of Organisms

PROKARYOTES

• A prokaryotic organism is a unicellular organism (such as a bacteria)

• Does not have an organised nucleus.

• Don't have any membrane-bound organelles. These are really simple cells.

EUKARYOTES

• A eukaryotic organism is an organism that consists of more than one cell.

• Humans have billions of cells, making them eukaryotic organisms.

• Eukaryotic cells have the capacity to contain many different kinds of organelles.

• These cells are complex, compared to prokaryotic cells!

Organelles Present in Both Cells

• NUCLEUS: Contains DNA that gives the cell all its instructions

• CELL MEMBRANE: A layer of the cell that controls the entry/exit of some substances (e.g. lets oxygen in so aerobic respiration can occur)

• CYTOPLASM: The jelly-fluid that fills the cell. Many reactions occur here

• CELL WALL: Present only in plants. Made of cellulose and gives cell a rigid structure

• ENDOPLASMIC RETICULUM: The site of protein synthesis if ER is rough, if it is smooth then fats and hormones are produced and transported to where they are needed

• MITOCHONDRION: the site of aerobic respiration (where food/nutrients turns into energy). Anaerobic respiration occurs in the cytoplasm

• CHLOROPLASTS: Present only in plants. The site of photosynthesis (using energy from the sun to turn water and carbon dioxide into glucose (food))

• GOLGI BODY: Packages proteins for secretion (release) from the cell

• RIBOSOMES: The site of protein synthesis (where proteins get made)

• VACUOLE: big in plant cells (helps maintain structure), small in animal cells. Holds water and stores nutrients if needed.

Respiration Process

• Respiration can either occur in the presence of oxygen (aerobic respiration) or in the absence of oxygen (anaerobic respiration)

There are three main stages in the process

• Glycolysis (breaking of the glucose molecule)

• Krebs Cycle (where the H is pulled off the remaining molecules leaving

CO, behind as a waste product)

•Electron transfer chain (most of the ATP is made here)

Glycolysis happens in the cytoplasm of the cell, however the other two steps happen in the mitochondria.

The ATP-ADP Cycle

• In respiration, glucose is rapidly broken down in a series of steps controlled by enzymes.

• The end product is Adenosine Tri Phosphate (ATP). This is a high energy molecule and it is in this form that cells store chemical energy.

• When ATP is converted to ADP (adenosine diphosphate) energy is release and used for cell processes.

Stage 1: Glycosis

• Occurs in the Cytoplasm

• Glucose (C₆H₁₂O₆) broken down into 2 pyruvate molecules (C₃H₄O₂). Does not require oxygen (anaerobic). - Pyruvate required for next two steps

«H₂O is also produced.

• Energy from the bonds broken in glucose are used to add a phosphate to two molecules of ADP (to make ATP)

• Result:

• Substrate: Glucose

• Products: 2 Pyruvate molecules, H2 and 2 ATP molecules

• NADH is like a taxi and picks up the hydrogen atoms and takes them to the matrix.

Stage 2: Kerbs Cycle

• Occurs in the Matrix

• Pyruvate (C₃H₄O₂) is fed into a complex cycle that rearranges the pyruvate atom to form carbon dioxide (CO2) and H atoms. CO2 is waste, H atoms are moved to the cristae.

• The breaking of bonds here also allows for two more ADP's to be turned into ATP.

Result:

• Substrate: 2 pyruvate molecules.

• Products: Carbon dioxide, hydrogen atoms and 2 ATP molecules

• NADH is like a taxi and picks up the hydrogen atoms and takes them to the cristae.

Stage 3: Electron Transport Chain

• Occurs in the Cristae

• H₂ atoms are ionised (become H+)

• The electrons are then passed along a series of acceptor molecules found on the cristae.

• The energy from the electrons doing this is used to convert more ADP to ATP (by adding a phosphate)

• Once the electron reaches the end of the chain it hops/joins back on to its Hydrogen atom and is expelled from the cell as water.